Category Top Description for Custom Post Type

Let’s say I create a custom post type called “Restaurants” with a slug of /restaurants. Then within that custom post type I create several categories, like Fast Food, Italian, etc.

When I create those categories I can set a Category Top Description, so when I visit /restaurants/italian it will show a custom description at the top of the page where I can put ads and such.

But how can I set the Category Top Description for /restaurants itself? I can’t find a setting for that, and it’s the most important place for me to be able to enter custom text.

If it can’t be done in the current admin panel, what would be the most appropriate hook to use to add my own text to these pages? I’m using Supreme Directory Theme if it makes any difference. I’m hoping for something like:

add_filter('geodir_above_cat', 'geodir_above_cat_custom', 10, 1);
function geodir_above_cat_custom($cat){
  if($cat == THE_RESTAURANT_CAT){
    return 'My category top description text here.';
  }
}

Thanks for your help.